Field effect-type transistors have been used for many years in the field of amplifier circuitry, and provide a very useful device for integrated circuitry. The use of field effect transistors is widespread, as such, transistors show repeatable characteristics and useful and versatile amplifying properties.
Unfortunately, field effect transistors typically suffer from drawbacks when used within radio frequency (RF) amplifier circuits. In particular, the harmonic distortion caused in the signals being amplified at radio frequencies will tend to increase with the signal amplitude. This limits the dynamic range for which the field effect transistor can be used, and consequently limits the dynamic range of the amplifier circuitry.
In particular, the most critical source of the distortion is caused by the third harmonics of the signal. Such harmonics lie with frequencies that are quite near those of the frequencies associated with the actual signals themselves, and in light of this cannot be suppressed by simple filtering. Whilst it has been possible to improve the above harmonic distortion in prior art field effect transistors, this is at the expense of an increased power consumption. The most typical approach to improving the distortion characteristics, is by increasing the bias current which is used within the amplifying transistor. Clearly, this increase in bias current leads to the increase in power consumption, which brings with it low performance when many such amplifying circuits are provided, with additional problems associated with heat dissipation, and the like.